This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Objective: To evaluate the impact of AIDS virus evolution on the design of vaccines, we will determine whether mutations that facilitate AIDS virus escape from CD8+ T-cell responses also affect viral fitness in vitro and in vivo. We are also attempting to determine the major factors that contribute to elite control of AIDS virus replication. We have recently developed an animal model of elite control in Mamu-B*08+ Indian rhesus macaques. Remarkably, 50 percent of Mamu-B*08+ Indian rhesus macaques control replication of SIV, and Mamu-B*08 and HLA-B*27 bind similar peptides. Thus, these Mamu-B*08+ macaques are ideal for modeling human Elite Controllers (ECs). Understanding why ECs suppress viral replication should facilitate the development of an effective HIV vaccine. PROGRESS: Elite controllers of HIV and SIV are studied with the goal of understanding immunological mechanisms underlying successful control of immunodeficiency virus replication. Elite control is associated with particular MHC class I alleles, implicating CD8+ T cells as mediators of control. Since in vivo CD8+ cell depletion in two Mamu- B*08+ EC rhesus macaques results in an immediate increase in viral replication, CD8+ lymphocytes are likely important for control in these ECs. Interestingly, SIVmac239Dnef-vaccinated Mamu-B*08+ macaques exhibit almost complete control of a heterologous SIVsmE660 challenge. Additionally, HLA-B*27 and Mamu-B*08 bind the same peptides requiring an arginine at position 2, and antigen-specific Mamu- B*08-restricted CD8+ T cell responses dominate the acute phase in ECs. A mutant SIV virus, with functional T cell escape mutations engineered into eight of the 14 described Mamu-B*08-restricted T cell epitopes, greatly reduced the incidence of elite control when introduced into a cohort of 10 Mamu-B*08+ macaques. Only 20 percent of these animals controlled replication of the mutant virus, in contrast to 50 percent of Mamu-B*08+ animals which typically control viral replication. These results implicate MHC class I-bound peptide-specific memory CD8+ T lymphocytes in control of viral replication in Mamu-B*08+ rhesus macaques. We have used a novel DNA sequencing platform, Roche 454 pyrosequencing, to sequence individual viral quasispecies early in acute SIV infection of Mamu-B*08+ macaques. These studies revealed that one of the most immunodominant Mamu- B*08-restricted CD8+ T cell responses, Vif RL8, may be critical for control of viral replication. Only 54 percent of Mamu-B*08+ macaques will become ECs. A comparison of the viral loads of Mamu-B*08+ macaques that control virus with those that do not reveals that circulating quantities of virus are not different between the two groups within the first four weeks post-infection. Interestingly, we discovered that the virus in animals that fail to control viral replication contains many different individual quasispecies with escape mutations in the Vif RL8 epitope as early as three weeks post-infection. Elite controllers do not exhibit such mutations. No other significant differences were seen in the other Mamu-B*08-restricted epitopes at these early time points post-infection. These data suggest that viral escape from a single immunodominant CD8+ T cell response may determine outcome with regards to viral control in Mamu-B*08+ macaques. To follow up this observation and previous observations regarding the importance of acute phase immunodominant Mamu-B*08-restricted CD8+ T cell responses, we will be carrying out a vaccination experiment in the coming months to evaluate the importance of these immunodominant responses. We will vaccinate two groups of eight Mamu-B*08+ animals with a Yellow Fever 17D prime, Adenovirus serotype 5 boost strategy which we have previously shown effectively generates robust CD8+ T cell responses. One group of eight animals will receive the vaccine with inserts containing the three most immunodominant Mamu-B*08-restricted CD8+ T cell epitopes: Vif RL9, Vif RL8 and Nef RL10. The other group of eight animals will receive vaccines containing control segments of the SIV proteome including another portion of Vif and a section of Gag. These regions do not contain any known Mamu-B*08- restricted CD8+ T cell epitopes. We hypothesize that preparing the immune systems of the group of animals receiving the immunodominant epitopes to generate these effective CD8+ T cell responses prior to infection will boost the incidence of elite control so that all infected Mamu-B*08+ animals receiving such a vaccine will become elite controllers, whereas only four of the eight Mamu-B*08+ control vaccine animals will control viral replication. This experiment will directly test our assertion that certain Mamu-B*08-restricted T cell responses are critical for viral control and will direct more comprehensive study at these specific T cell responses as models for effective vaccine-induced T cell responses. This research used WNPRC Animal Services, Genetics Services, and Immunology &Virology Services.